The invention relates to a system for the relative rotating position change of a shaft with respect to the driving wheel, particularly of a camshaft of an internal-combustion engine.
Such a system is known, for example, from International Patent Document WO 95/31633. This document describes a system for the rotating position change of the camshaft of an internal-combustion engine, in which the camshaft is non-rotatably connected with an internal geared wheel which has radial webs which divide assigned cells of a cell wheel into two pressure spaces respectively which operate against one another. By way of a chain drive or belt drive, this cell wheel is driven by the crankshaft of an internal-combustion engine. Pressure is admitted to the respective pressure spaces by way of a control valve which is constructed as a 4/3-way valve and by means of which the pressure spaces are connected as a function of the desired rotating position change with a pressure medium pump or a pressure medium tank. For this purpose, one pressure line respectively leads from this control valve to all pressure spaces acting in the same direction. Furthermore, one return valve respectively is arranged in these pressure lines which can be hydraulically unblocked and whose blocking effect can in each case be abolished by the pressure in the other pressure line. In the neutral position of the control valve, while neglecting the leakage losses, a hydraulic clamping can be achieved of the two components, which can be rotated relative to one another, by way of these return valves. However, such a system requires relatively high expenditures. Furthermore, during the adjusting operation, because of the almost unthrottled connection of one pressure space group with the pressure medium tank, unintended position deviations and inaccurate or fluctuating adjusting operations can occur.
In addition, from U.S. Pat. No. 4,858,572, a system is known for the rotating position change, in which an internal part is non-rotatably connected with the end of the camshaft and has on its exterior side several radial slots which are distributed along the circumference and in which wing elements are guided in a radially displaceable manner. This internal part is surrounded by a cell wheel which has several cells which can be acted upon hydraulically and which, by means of the wings, are divided into two pressure spaces which act against one another upon the latter. By admitting pressure to these pressure spaces, as a function of the pressure difference, the cell wheel can be rotated relative to the internal part and thus relative to the camshaft. Furthermore, one piston respectively, which can be acted upon hydraulically, is guided in the cell wheel in two radial bores in defined angular positions, which piston can be pushed into a radial indentation of the internal part in the assigned end position of the system. By means of pressure spring elements, these pistons are acted upon in the direction of the internal part and can be displaced in the opposite direction by the hydraulic action upon the bores in the internal ring. By means of these spring-loaded pistons, the system is to be locked in one of its two end positions as long as the pressure for acting upon the pressure spaces does not reach a defined level. Only when a defined pressure level is reached, will the pistons be pushed back against the effect of the pressure springs and will permit a rotating of the internal part relative to the cell wheel. By means of such a system, rattling noises, among others, are to be avoided when the internal-combustion engine is started, which rattling noises may occur as the result of changing torque loads during the start and the operation of the internal-combustion engine.
In contrast, the invention is based on the object of improving the system of the above-mentioned type for the relative rotating position change of a shaft with respect to the driving wheel such that it is constructed in a simpler manner and at more reasonable cost and permits a rotating position change which is free of fluctuations. The main object is the avoidance of the use of several high-expenditure high-cost control valves.
Furthermore, when the internal-combustion engine is stopped and in the steady-state operation of the system, a simply operating hydraulic locking is to be permitted.
According to the invention, this object is achieved by providing a system for the relative rotating position change of a shaft with respect to the driving wheel, particularly of a camshaft of an internal-combustion engine, having an adjusting arrangement with two pressure spaces acting against one another, having a pressure medium pump, a pressure medium tank and at least one control valve, during the adjusting operation, one pressure space being connected with the pressure medium pump and the other pressure space being connected with the pressure medium tank, characterized in that, at the start of an adjusting operation, one pressure space is connected with the pressure medium pump before the other pressure space is connected with the pressure medium tank.
Because of the fact that, when the adjusting operation is initiated, one pressure space is connected with the pressure medium pump, before the other pressure space, which operates in the opposite direction, is connected with the pressure medium tank, it is prevented that the pressure drop on the side to be relieved takes place faster than the pressure rise on the opposite side. This results in a damping or throttling of the outflow side by means of which an adjustment is prevented which is in advance of the pressure rise. The adjusting operation thereby becomes damped and more precise. Such a control of the pressure admission and pressure relief permits the avoidance of high-expenditure damping devices and allows in a simple manner a controlled regulating or a controlled conversion of the adjusting movement as the result of the pressure control.
A damping or throttling on the outflow side, which functions during the whole adjusting operation, is achieved in that the control cross-section to the pressure medium tank during the adjusting operation is always smaller than the opening cross-section to the pressure medium pump. As a result, during the whole adjusting operation, an advancing before the pressure rise is prevented so that a very precise position assignment and a largely fluctuation-free adjustment is possible during the whole adjusting operation.
A particularly advantageous construction of the system for the relative rotating position change which is reasonable in cost is obtained if the inflow control as well as the outflow control for the assigned rotating direction is controlled by way of a common valve element of the control valve.
Such a system for the relative rotating position change will be even more simplified and lower in cost if a common control valve and a common valve element are utilized for both directions of the rotating position change.
In this case, the control valve may be constructed in a particularly advantageous manner as a 4/3-way valve, the valve element acting for the inflow and outflow control for both rotating direction being constructed as a valve slide.
Additional advantages and advantageous further developments of the invention are found in the description.
An embodiment of the invention will be explained in detail in the following description and drawing.